I have always talked about this. When bitcoin reached to $20k or so levels the big whales made it out big, than they recollected when it dropped back. This was the phase 1. Than the short futures came up, which meant that if rich people sold bitcoin they would have fiat capital to play with, when they sold all of their coins (or some of it) they would cause a small drop in the price and with enough media at their hands they could create a fud around that drop which would result in even further drop from scared people.
However those rich whales who sold their coins to gain capital spent that capital on buying shorts during that time. Even though bitcoin is dropping, these people would have been profiting from it thanks to short futures.
I definitely believe that the futures are an incentive for whales to anonymously manipulate the price. I just don't really see how this could be done, but it does make a lot of sense. Once more capital enters this space then manipulation like this would be significantly harder to achieve. Once massive hedge funds, like BlackRock for example, enter the Bitcoin space the market will gain a ton of depth. These hedge funds would likely only diversify a small percentage of their holdings into Bitcoin which means two things:
1. Since Bitcoin would be a small percentage of their holdings, Hege funds themselves wouldn't waste their time attempting to manipulate the BTC market, as they know its a long-term holding and any manipulation in the short term would be small gains.
2. Even a group of whales wouldn't be able to pool enough money together to move the market in any meaningful way, as the Bitcoin market would likely be worth around $1 trillion by this time and a significant amount of money would be required to move the market.
Right now, the CBOE futures are something that we only have to worry about in the short term. It's only a matter of time for a Bitcoin ETF to get approved and manipulation like this to become significantly more difficult.
I could be wrong of course, but this is my thought process on the future of Bitcoin and the risk of manipulation.